A vehicle gearbox in a gear reduction assembly form is, with respect to construction and especially with respect to price, a very advantageous solution to gear boxes. Generally, they have a countershaft situated parallel to the input shaft and a drive shaft. The power flows over a set of gears from the input shaft to the countershaft and from there over another set of gears to the drive shaft. One of the gear sets, which is involved at all speeds and is referred to as a constant, has two fixed gears attached to each other and are situated on each of the countershafts or on the input shaft or the drive shaft, as the case may be. The other set of gears has an idler and a fixed gear. Each is related to one speed and is shifted so that the idler becomes engaged with the appropriate shaft through a separating clutch mechanism. The set of gears for the reverse speed, also referred to as the reversing gear, also includes an intermediate gear which, on the one hand mates with an idler and, on the other hand, with the fixed gear and thus reverses the rotating direction of the drive shaft with respect to the input shaft.
Generally, the separating clutch mechanisms are arranged so that they can be engaged in succession by a driver using the mechanical actuating elements in that he engages a gear shift lever in two mutually arranged perpendicular movement levels. The motion at the first movement level selects two gears of a gearshift gap and one of the selected gears is shifted by the motion in the second movement direction.
In order to drive a vehicle engine within an optimal operating range, it is desirable to have a transmission with many gear shifts, whereby the progressive ratios between the individual gear shifts, from the highest to the lowest gear, should increase progressively. In this way, by using a fine graduation, the driver can fine-tune the number of revolutions to the speed of the vehicle. Furthermore, the entire transmission range of the vehicle gearbox between the first and the highest gear should be wide, so that the relationship of the transmission range to the number of gears should be relatively large in order to keep construction costs low. Such a vehicle gearbox can be made at a justifiable expense with up to six forward speeds.
The construction cost of a vehicle gearbox with several forward speeds can be further reduced in that multiple uses can be made of individual gear sets so that they may be used to create different speeds. For example, in the case of a group of gearboxes consisting of the main gearbox group, a supplemental gearbox group consisting of two or more gear sets will go either up- and/or downstream, so that we can achieve the maximum number of gears in the vehicle gearbox from a combination of gear sets of the supplemental gearbox groups from the product of the number of gears of the individual gearbox groups. The progressive ratio between gear sets of the supplemental gearbox group will thus be adjusted to the progressive ratio between the gear sets of the main transmission groups so that an overall usable gradation of the vehicle gearbox will be achieved. Based on the group design of the vehicle, generally only a geometric, rather than a progressive gradation of the entire transmission ranges is possible with gearboxes, since the multiple use of the gear sets of the main gearbox group are repeated many times because of the progressive ratios of the main gearbox group.
Generally, while the supplemental gearbox group will be designed as a so-called split gearbox group, the progressive ratios of the main gearbox group are subdivided as so-called area gearbox groups of the transmission range of the main gearbox group and expanded up- or downwards. While the main gearbox group is usually designed so that it can be shifted with mechanical means by hand power, the supplemental gearbox group can be operated by external power, for example, electrically, hydraulically, or pneumatically. Such gearbox groups for transmissions with eight or more gears are known from the Construction Books, Band 26, by Johannes Looman, Cogged Wheel Transmissions, 1970 Springer Publishing, Berlin, pp. 181 ff.
Furthermore, due to the intensity of the competition, it is necessary to design gearbox families for different power requirements and interchange many of the same parts in order to reduce costs. It is known that gearboxes are built according to the modular building block principle for this reason.
The basic goal of the invention is to provide a vehicle gearbox in a six-gear version and an eight-gear version with the same external measurements by using a large number of the same parts.